A cooling system for removing heat energy from a part being worked, i.e., a "work piece," must be able to remove a sufficient amount of heat energy from the work piece to prevent heat-related damage to the work piece. Heat-related damage includes partial or complete melting of portions of the work piece resulting in plastic deformation. Another form of heat-related damage results when excessive heat distorts the work piece or the tool by causing portions of the work piece or the tool to physically expand in size. When portions of the work piece or tool expand in this way it can make it extremely difficult to adjust cutting tolerances to compensate for the material expansion especially when the work piece or tool comprise materials with different thermal expansion coefficients.
Current systems that cool work pieces typically employ a lubricant fluid bath. Such fluid baths control heat build-up in a work piece by reducing the friction generated between a cutting element, such as a grinding surface, a drill, a lathe or a saw, and the work piece. Fluid baths also dissipate heat by convective heat transfer, i.e., by absorbing heat energy and carrying it away from the work piece.
Fluid baths of this type also carry away fragments of the work piece--fragments that have separated from the work piece in the process of being worked. The fluid must, therefore, be filtered to remove these fragments. In addition, work pieces that have been worked while being cooled by such a bath must, in most cases, be cleaned to remove the cooling fluid before the finished parts can be put to their intended use. Properly reclaiming, disposing of and otherwise accounting for fluids used in these cooling bath systems in an environmentally responsible manner can be difficult, expensive and time-consuming.
At least one fluid bath-type cooling system avoids the problem of filtering fragments by circulating cooling fluid within the work piece itself. U.S. Pat. No. 4,513,538 issued to Wolters et al. on Apr. 30, 1985 discloses a cooling system in an apparatus for superfinishing thin-wall metal work pieces. With this system a fluid coolant directly contacts a surface of a work piece, i.e., an interior surface directly opposite the work piece surface being machined.
Another type of system that has been disclosed for cooling work pieces circulates a fluid coolant through the tool that works the work piece. Because tools of this type typically must move in relation to supporting machine elements, it can be difficult, time consuming and expensive to design, construct and maintain systems that circulate fluid in and out of such tools without leakage.
An example of a system that circulates fluid through a tool is disclosed in U.S. Pat. No. 5,127,196 issued to Morimoto et al. on Jul. 7, 1992. The cooling system disclosed in this patent is used in an -apparatus for planarizing a dielectric formed over a semiconductor substrate. A fluid coolant is circulated in and out of a machining tool in the form of a hollow grinding table. The fluid cools an abrasive upper surface of the grinding table from within the table. The table rotates in relation to the semiconductor substrate and its abrasive upper surface grinds the dielectric-coated face of the substrate.
Another example of such a system is disclosed in U.S. Pat. No. 4,450,652 issued to Walsh on May 29, 1984. The Walsh patent discloses a cooling system for an apparatus that polishes semiconductor wafers. Similar to the Morimoto et al. patent, this system passes cooling fluid through a grinding tool in the form of a turntable with an upper abrasive surface for grinding wafers.
U.S. Pat. No. 3,571,978 issued to Day et al. on Mar. 23, 1971 discloses a lapping machine having a lapping tool in the form of a hollow pressure plate through which a cooling fluid is circulated. The work to be lapped is placed between the pressure plate and a lapping table.
What is needed is a system that cools work pieces without wetting any surface of the work piece and without including a fluid coolant circulation system within the work piece or the tool that works the work piece.